Improve core shader warning usability - #3903

Linked Issues

Closes #2191.

Proposed Changes

This change keeps core-shader compatibility problems actionable without covering normal gameplay with transient warnings:

• Keep the current resource-pack compatibility problems in memory so they remain available after resource loading finishes.
• Add a persistent compatibility-issues indicator to the main menu and pause screen.
• Add a dedicated details screen that names each affected pack, explains the severity and likely impact, lists the detected shader files, and points the player to either Resource Packs or the compatibility documentation.
• Distinguish server-provided packs from local packs so the suggested resolution and available actions match what the player can actually change.
• Stop displaying the core-shader console toast over arbitrary screens. The compatibility report is still written when the detected problem set changes.
• Run the scan after the resource reload future completes so the UI cannot retain stale pack names from the previous resource set.
• Keep the empty state concise and position the pause-screen indicator away from the vanilla top-right controls.

The indicator provides a durable place to review the problem from an actionable screen, while resource reloads and ordinary gameplay remain unobstructed.

Validation

• Ran ./gradlew build with OpenJDK 25.0.2: all 35 tasks completed successfully for the common, Fabric, FRAPI, and NeoForge projects.
• Ran the Fabric development client with an enabled test resource pack containing assets/minecraft/shaders/core/rendertype_solid.vsh.
• Confirmed the scanner identifies the pack and writes the affected shader path to the compatibility report.
• Confirmed the working tree passes git diff --check.

The project currently has no automated test sources covering the resource-pack scanner or screen flow, so this change relies on the full multi-loader build and manual development-client validation.